Anticancer agents, nucleoside analogs

Nucleoside analogs substituted at the C-5 position of the pyrimidine base have been identified as anfiviral and anticancer agents, hi this context new... 

Cytosine arabinoside (69), a synthetic analog of the C-nucleosides spongouridine (70) and spongothymidine (71) from the sea sponge Cryptotheca cripta, was the first and, so far, the only marine-derived compound used routinely as an anticancer agent (110). However, a number of chemically diverse natural products from marine sources have been progressed to clinical trials. The three most advanced compounds are in phase II trials ecteinascidin-743 (72), a tetrahydroisoquino-... 

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